what this command will do is preventing the routes from entering the routing table, and as a result of that:the ABR is re-generating a type-3 lsa, the Route must be in the routing table,so this command remove a route from routing table so type-3 will not be created.

R2(config-router)#distribute-list prefix block172 in

now i think you got the idea about they work.

the question will be where to add them, here or there and why.

check this diagram : i have added all possible points to use the above commands, you will only use one of them and that will depend on the situation.

on point 2 :

distribute-list in : remove the route from routing table + it will not be sent to area 2 or 3

filter-list out : filter a route from being sent to any area ( this route can be intra or inter or a summarized )

filter-list in : will filter a route going to a specific area.

on point 1 :

distribute-list in : remove the route from routing table but the route will continue to be flooded (blackhole)

area range : will create a summary but this summary will not be advertised to any area

filter-list out : will filter the router from being sent to any area , imagine that R1 is connected area 4 + area 0

filter-list in : this will prevent the route to be send to specific area’s

external routes

1.Summary-address + not advertise

so this command will create external summary, but this summary will not be injected.